Method and device for the analysis of hydrogen in steels



July 14, 1970 -n ET AL 3,520,71

METHOD AND DEVICE FOR THE ANALYSIS 0F HYDRROGEN IN STEELS Filed June '7, 1968 a-Lu-us-I. 1: a

FIGS

United States rm. or. @0111 3/08 U.S. Cl. 73-23.1 11 Claims ABSTRACT OF THE DISCLOSURE Method and device for the analysis of hydrogen in steels which comprise heat extraction of said hydrogen in a carrier gas and successive gas-chromatographic definition thereof, wherein the carrier gas is constantly fed from a single source and, through two conduits in parallel, is divided in two fractions, the first of which flows towards the measuring side of a katharometer, while the second flows towards the reference side of same and is then used for extracting the gases from the test tube; such an analysis is performed in four successive steps, that is respectively: a washing step, during which the second fraction of carrier gas downstream of the reference side of the katharometer is conveyed for washing to an extraction chamber containing the test tube in series therewith to a sampling tube. a withdrawing step, during the heating of the test tube, wherein the second fraction of carrier gas, mixed with the gases removed from the test tube, is conveyed to fill a container with deformable walls; a sampling step, wherein the second fraction of carrier gas is discharged into the atmosphere downstream of the extraction chamber, and the contents of the container with deformable walls are conveyed to the sampling tube; a measuring step during which the sampling tube, containing the gas mixture to be analyzed at atmospheric pressure, is fed with pure carrier gas, consisting of the first fraction, while its outlet end feeds in turn to a chromatographic column in series with the measuring side of the katharometer.

BACKGROUND OF THE INVENTION For a definition of hydrogen in steel samples of 1-15 grs. in the form of small bars to be subjected to embrittlement mechanical tests, owing to the low basic contents of hydrogen, about 0.2 ml./ 100 g., it was necessary to realize a method and device particularly responsive and exact.

Among the various methods are of particular interest those based on the extraction from solid phase in a current of carrier gas, which permits operating on samples of considerable size with all the resulting advantages, as the reduction to a minimum of absorptions and losses through exposure to the air. Further, such methods are much simpler than the ones based on extraction under vacuum which require very expensive and complex devices.

The extraction time by said methods was not found to be remarkably longer than that of extraction in solid phase under vacuum, as the extraction speed is controlled mainly by the dilfusion of hydrogen into the steel.

Various methods are based on the heat extraction by reactive atmospheres, but said methods have been replaced by those of extraction in inert gases.

Hayn, already in 1903, tried the definition of hydrogen in steels by heating the sample in a nitrogen current and proportioning, by gravimetric methods, the water formed by combustion on copper oxide.

3,520,171 Patented July 14, 1970 Such a method was successively taken up by Sanahan and Cooke, who proportioned the water obtained by combustion by titration with the Karl Fischers reactive.

Zitter and Swarz also describe an apparatus based on the same principle used for the extraction of hydrogen on solid samples 50-100 g.).

The value of the blank found by the above-mentioned people corresponds to 0.2 ml. per hour.

Obviously, by said blank it is not possible to define values which can be of interest for the applicant. Giegerl proportions the water obtained by combustion of the extracted hydrogen, by causing it to react with graphitic carbon at 1200 C. and obtaining therefrom hydrogen and CO.

The obtained CO is transformed to CO by the Schutze reactive. The quantity of CO equivalent to H is finally defined by the Coulombs metric method in an Olsen- Abresch device.

Such a method is found to be complicated and scarcely exact (blank 0.4 ml. per hour).

Such difficulties are sufficient to lead to the choice of other methods for proportioning hydrogen.

Rooney and Barr defined successfully hydrogen in steels by heating the sample for one hour at 600 C., using at atmosphere of N in a closed cycle and proportioning hydrogen by means of a thermic conductivity cell (katharometer). Such a technique successively developed by Ramsley appears to be not suitable for current analysis, as it requires the use of pumps in order to recycle the gas and thus offers scarce advantages with respect to the conventional method of extraction under vacuum.

In the apparatus realized by Cambridge Instrument Co. Ltd. for BISRA, the extraction is effected in an argon closed circuit at 650 C., by making the argon-hydrogen mixture recycle by natural convention, said mixture being continuously measured by a katharometer.

The silica tube initially used was found to have a certain permeability with respect to hydrogen, and was thus replaced by a Regalox ceramic tube.

The time required for the definition was 30-40 minutes for cylindrical test tubes with a diameter of 13 mm., and decreased down to 15 minutes for test tubes with a diameter of 6.5 mm. Argon was dried at the inlet of the extraction pipe by making it pass through a tube of anhydron.

A second layer of 3 mm. of anhydron inserted at the inlet of the katharometer removed the steam present in the extracted gases, preventing the transformation thereof to hydrogen by reaction with the test tube surface during the recycle.

With reference to said method, it can be noted first that even the particles of oxygen in the gas are to be removed, as they can combine with hydrogen to form water which is then kept by the anhydron. Further, the anhydron is not very efiicient in keeping water.

Such an apparatus has further the disadvantage that it gives the value of hydrogen in balance for the sample at 650 C. in the presence of a certain mixture of hydrogen in argon, and not the actual value of the total hydrogen.

The same remarks may be made for the apparatus realized almost at the same time by Sandrinelli and Guarnieri which provides for the gas-chromatographic analysis, in a separate step, of the mixture obtained for the extraction in argon by natural convention, and collected on mercury in a gas burette.

The apparatus realized by BWRA also uses a katharometer for proportioning hydrogen. In such a case, the extraction takes place in a continuous flow of argon of 11 ml. per minute without any recycle.

For samples of 5 g. the extraction time, at 650 C., is

established at about 15 minutes. The removing of humidity from the carrier gas is performed through an anhydron absorber arranged upstream of the extraction chamber.

Such a method gave good results, but it is subject to serious disadvantages, that is the uncertainity of the measure owing to a possible displacement of the zero line, the impossibility of repeating the measures and the fact that there is in any case a sum of blank due to, besides the re maining humidity in the carrier gas, the impurities which are occluded or absorbed or which in any way develop during the extraction treatment at 650 C.

From the point of view of the analysis of the extracted gas, the apparatus of Hancard and Marot is better. By the latter apparatus the gas extracted at 1000 C. is collected in a gas burette using mercury as a confining liquid, and then part of the mixture is taken up to be analyzed by the gas-chromatograph. The carrier gas used (argon) is dehydrated upstream of the extraction pipe by means of a coiled pipe immersed in a cooling mixture consisting of Dry Ice and acetone.

The more serious disadvantage of such apparatus, besides the insufficient purification of the gas, is represented by the method for collecting the extracted gas which has the disadvantage of the difficulty of preventing gas losses, as a small difference in the level of mercury always causes remarkable difference in pressure. Not smaller are the difiiculties of the handling and thus of the operation of washing and homogenization of the sample collected. Other disadvantages may result in that it is difficult to have clean and dry surfaces of mercury.

SUMMARY OF THE INVENTION In order to avoid the disadvantages of the methods cited in the above short list, the method and device according to the present invention were realized, which have the particularities described herebelow and which have been found fully suitable for the applicable requirements.

The method according to the present invention is characterized in that the carrier gas is constantly fed from a single source and, through two conduits in parallel, is divided into two fractions the first of which flows towards the measuring side of a katharometer, and the second towards the reference side thereof and is then used for extracting the gas from the test tube. Such an analysis is performed in four successive steps respectively: a washing step during which the second fraction of carrier gas downstream of the reference side of the katharometer is used for the washing of an extraction chamber containing the test tube and in series thereto a sampling tube; a withdrawing step during the heating of the test tube, wherein the second fraction of carrier gas, mixed with the gases removed from the test tube, is conveyed to fill a container with deformable walls; a sampling step wherein the second fraction of carrier gas is discharged into the atmosphere downstream of the extraction chamber, and the content of the container with deformable walls is conveyed to the sampling tube; a measuring step during which the sampling tube, containing the gas mixture to be analyzed at atmospheric pressure, is fed with pure carrier gas, represented by the first fraction, and its outlet end feeds in turn a chromatographic column in series with the measuring side of the katharometer.

The device suitable to embody the above method is of the kind comprising: a tank for the carrier gas; a katharometer provided with a measuring side and a reference side; an extraction chamber containing the test tube and passing through an oven for heating said tube; a chromatographic column fed with pure carrier gas in the washing and sampling steps, and fed with the gaseous mixture 'to be checked in the measuring step; a set of filters for purifying the carrier gas; said device further comprising: two conduits in parallel for feeding the carrier gas coming from the corresponding tank to the measuring and reference sides respectively of the katharometer; means for feeding in series the extraction chamber and a sampling tube with the fraction of carrier gas coming from the reference side of the katharometer; a container with deformable walls inserted in shunt between the extraction chamber and the sampling tube; controllable means for deflecting the gas or the gas mixture from the extraction chamber towards the atmosphere or the container with deformable walls; means for deflecting the content of said container with deformable walls towards the sampling tube; means for inserting the sampling tube into the inlet conduit of the first fraction of carrier gas just upstream of the chromatographic column.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a diagrammatic view of a device according to the invention;

FIG. 2 is a diagrammatic view, on a larger scale, of a detail of FIG. 1 and in particular the sampling valve in the position of washing, withdrawing and sampling;

FIG. 3 shows the same valve in the measuring position;

FIG. 4 is a diagrammatic sectional view of the outlet end of the extraction chamber taken on the line IVIV in FIG. 5;

FIG. 5 is a diagrammatic view taken on line VV in FIG. 4;

FIG. 6 is a diagrammatic sectional view of the assembly for stirring, filling and emptying the inner tube inserted in shunt between the extraction chamber and the sampling valve.

DESCRIPTION OF A PREFERRED EMBODIMENT The main characteristics of the present invention have been described in the summary of the invention.

However, in order to enable an expert in the art to embody the present invention completely and without any need of useless and expensive trials, it will be advisable to list herebelow some particular arrangements constituting part of the invention.

The mixture of the carrier gas with the gases removed from the test tube is closely mingled before being sent to the sampling tube. The second fraction of carrier gas, before being conveyed to the extraction chamber, is purified by means of a suitable set of filters the first of which of anhydron, ascarite and P 0 respectively, :by means of a small copper oven and finally by means of a further P 0 filter, the latter being arranged in series and being the last.

The carrier gas used consists of argon fed at a pressure of about 2 atmospheres, the flow of which inside each of the two sides of the katharometer is preferably adjusted at 15-20 ml. per minute. During the mentioned fourth measuring step, the sample is replaced and de-aerated by means of the flow of the second fraction of carrying gas.

In embodying the device it is further necessary to take note of the following requirements: the container with deformable walls consists of the rubber inner tube or bladder for a football. Between the extraction chamber and the reference side of the katharometer there are inserted a first filter of anhydron, ascarite and P 0 a purifying copper oven maintained at 450 C., and a second P 0 filter.

The mentioned device further comprises a six way and two position sampling valve by means of which, in the first position corresponding to the washing, withdrawing and sampling steps, it is possible to connect: the inlet conduit of the first fraction of carrier gas with the chromatographic column and then in series with the measuring side of the katharometer; the outlet end of the sampling tube with the atmosphere; the extraction chamber or the container with deformable walls respectively with the inlet end of the sampling tube. In the second position, corresponding to the measuring step, it is possible to connect by means of said sampling valve: the inlet conduit of the first fraction of carrier gas with the inlet end of the sampling tube; the outlet end of the sampling tube with the chromatographic column and then in series with the measuring side of the katharometer; the container with deformable walls to the atmosphere. The outlet end of the extraction chamber is connected to a plate movable between at least two positions; in the first of said tWo positions, the extraction chamber can be reached from outside for removing or introducing a sample, while in the second position the interior of said chamber is put in sealing communication with the outlet conduit of the chamber itself.

Said inner tube is contained within a rigid housing which is connected on one side with the atmosphere and on the other with a vessel for compressed air or other pressure fluid by means of a first valve and a second valve respectively, in such a way that, by acting suitably on said valves, it is possible to cause a mingling of the contents of the inner tube as well as, at due time, the washing, filling and emptying thereof.

The invention will be further described wth reference to the drawings.

With reference to FIGS. 1, 2 and 3: a gas-chromatograph 1 of known type is provded with a thermoconductivity detector with platinum wires and a two position and six way sampling valve 2 for injecting gaseous samples. The valve 2 has six ports 23, 24, 25, 26, 27 and 28. A sampling tube 22 is connected :between the ports 24 and 27 of the sampling valve.

The carrer gas (Argon UPP) is delivered from a bottle 3 at a pressure of 2.5 atmospheres through a first reducer 4 and purified through a P filter 5 and a zirconium sponge oven 6 at 750 C.

A second pressure reducer 7 is mounted on the chromatograph for reducing the pressure to 2 atmospheres; right after that the gas is conveyed to two systems of automatic flow adjustment 8 and 9. The deliveries obtained, equal to 17 ml. per minute on each side, may be read on flow meters 10 and 11. A portion of gas passes through a by-pass conduit 12 and then into the reference side 1b of the detector, at the outlet of which it is taken up and used as extraction gas. A further purification is obtained through a filter 13 of anhydron, ascarite and P 0 in that order, followed by a metal copper purification oven 14 at 450 C. and then by a P 0 filter 15.

The extraction takes place in an extraction chamber comprising a quartz pipe 16 heated at 650 C. by means of a resistance oven 17, provided with a port for the passage of said pipe and slidable on a carriage in transverse direction.

The gas upon coming out of the extraction chamber may be conveyed either to the atmosphere or collected into an inner tube or bladder for a football, by suitably acting on the two cocks 19 and 20.

On the measuring branch downstream of the system 8 for the automatic flow adjustment, the gas passes through the sampling valve 2 and a chromatographc column 21 formed by a stainless steel pipe, with a length of 2 meters and an inner diameter of 4.2 mm., filled with molecular sieves 5 with a granulometry of +40 meshes, the outlet of which leads to the detector. The column temperature is about C., that of the detector 225 C.; the current on the measuring bridge is of 300 ma.

After the introduction of the degreased and dry sample into the extraction chamber 16, the carrier gas is made to flow for about ten minutes, that is for the time necessary to obtain a good washing of the circuit.

During this step, the position of the cocks and the sampling valve is as follows: valves 19 and 20 are arranged in such a way as to convey gas to the sampling valve 2, the latter being in the washing and sampling position (see FIG. 3).

Then valve 20 is rotated so as to collect the gas within the inner tube 18 previously carefully washed by the carrier gas, and at the same time the extraction oven 17 is heated.

After waiting for 20 minutes, that is for the time necessary for the hydrogen extraction, valve 19 is rotated so as to convey to the atmosphere the gas coming out of the reference side of the chromatograph and, after a suitable homogenization by shaking the inner tube 18 for 5 seconds, valve 20 is arranged in such a position as to convey the gas collected within the inner tube 18 to the sampling valve 2 which has remained in the sampling position, as shown in FIG. 2.

After the washing of the valve conduit and tube, the gas from said inner tube 18 is stopped through valve 20, then after a few moments, so as to allow the pressure in sampling tube 22 to balance with the atmospheric pressure, the sample is injected by rotating valve 2 to the analysis position (see FIG. 3), in this way the measuring step is started.

With reference to FIGS. 4 and 5, the extraction chamber 16 is provided with a two way and two position valve 29 suitable to facilitate the sample loading and ejecting operations and to reduce the de-aeration intervals, arranged at the outlet end of the extraction chamber.

The valve 29 comprises a stainless steel disc 30 fastened to the extraction chamber 16 by means of a screw collar 31 which presses against a Teflon conical sealing ring 32.

On the disc 30 there is rotatably mounted a Teflon disc 33, having the same diameter and thickness, provided with a conical bore 34 connected to valve 19 and a port 35 suitable for the introduction and removing of the samples.

The disc 33 is free to rotate about an axis 36 under suitable control. The device operates in the following way: in the step of removing the preceding sample and introducing a new sample, the valve disc 33 is in a position rotated with respect to the position shown in FIGS. 4 and 5. Therefore, the extraction pipe is open into the atmosphere. After the sample has been introduced and drawn to the extraction position by an electromagnet, the Teflon disc 33 is made to rotate 90 to the shown position.

The washing operation is started with the valve 29 in the position shown in FIGS. 4 and 5. Valve 29 remains in this position in the successive operations of extraction and withdrawal of the hydrogen and further in that of analysis which is made to coincide with that of the sample cooling.

With reference to FIGS. 6: in a particular embodiment the inner tube 18 is contained in a rigid box 37 provided with a valve 38, connected to a reservoir of compressed air, and with a valve 39 for connecting the inside of the container 37 to the atmosphere.

The device works as follows: in the sampling step, valves 20 and 39 are open and valve 38 is closed, therefore, the pressure of the extraction gas inflates the inner tube 18 which in this way is filled up.

In the homogenization step, valve 20 is closed and valves 38 and 39 are opened and closed alternately at intervals of two minutes, so as to provide a series of light blows which cause the inner tube to be shaken.

In the injection step, valves 20 and 38 are opened, while valve 39 is closed so that the pressure exerted by the compressed air on the inner tube 18 causes the gas contained therein to flow out through the sampling valve. The pressure of the compressed air is selected so as to be sufficient to make the gas contained in said inner tube to overcome the resistance exerted by the load losses of the sampling system.

By the described method and device the following advantages are obtained:

(a) A remarkable simplification of the apparatus, as with a single bottle of carrier gas it is possible to perform both the extraction and the analysis; in this way the various pressure reducers and indicators necessary for the other arrangements are made unnecessary;

(b) Saving of gas, as the same quantity of gas used for the normal operation of the gas-chromatograph allows also the withdrawing of the sample for the analysis;

() Facility of operation in the calibration step;

(d) The carrier gas for the extraction is the same as the one for the analysis, except for a further purification from particles of components, such as oxygen and humidity, which may alter the results and may simply come from contamination by the chromatographic circuit.

The further purification of the extraction gas is necessary as, in a series of preliminary tests, the sample was, after the extraction treatment for 20 minutes at 650, clearly oxidized.

The first time it was tested, a system comprising an absorber of anhydron, ascarite and P 0 in that order followed by a metal copper oven at 450 C. reduced the sample oxidation considerably, but the disadvantage caused by further particles of humidity still remained.

Such a phenomenon was evident from a series of tests which were performed in order to define the value of the blank in samples already subjected to a first extraction process. Such a blank for hydrogen coming surely from particles of humidity in the gas at the inlet of the extraction oven, remains even after a long maintenance of the sample at the extraction temperature.

Such a disadvantage could be removed only by placing some milligrams of P 0 at the outlet of the copper oven (that is just before the extraction chamber).

As already said in the introductory paragraphs, the factor which controls the outflow of hydrogen from the test tube is the diffusion speed of the atomic hydrogen inside the test tube. Such a speed is a function of the temperature and is independent, within certain limits, of the flow of carrier gas. Hence, the interest is operating with low deliveries in order to obtain a mixture richer in hydrogen and an easier purification of the gas.

On the other hand, a flow which is much too low results in obtaining, for the prefixed extraction time, a gas volume not suflicient to allow a careful washing of the piping and the sampling valve, and would further prevent the possibility of repeating the measuring. Such considerations led to the choice of a delivery of 17 ml. per minute. For flows comprised between 13 and 29 ml. per minute with a molecular sieve column of 2 meter length and 4.2 mm. diameter at 30, the most suitable volume of the tube of the sampling valve is found to be 5 ml. For higher sample volumes, saturation phenomena of the column start to appear with asymmetric and distorted tips and with insuflicient separation.

Therefore, 5 ml. was adopted as the standard volume of the sampling valve tube.

The choice of the inner tube of a football for collecting the extracted gas is due mainly to the simplicity of the system, particularly with reference to the starting washing operations and the likewise important operation of homogenization of the sample before the analysis (such operations, as it will be seen herebelow, may be easily rendered automatic).

As far as the diffusion of gas through the rubber is concerned, theoretical considerations and laboratory tests have ascertained that such diffusion does not affect the analysis of the test tube within the limits of the required exactness.

Although an embodiment of the present invention has been described and illustrated by way of example only, many changes and variations may be made in embodying the invention.

What we claim and desire to secure by Letters Patent is:

1. A method of analyzing the hydrogen content of steel by means of heat extraction in a carrier gas and successive gas-chromatographic definition comprising: feeding carrier gas constantly from a single source, dividing said carrier gas into a first fraction and a second fraction, and performing an analysis in four successive steps comprising: a washing step in which said first fraction of carrier gas is passed through a chromatographic column and the measuring side of a katharometer and said second fraction of carrier gas is passed successively through the reference side of a katharometer, an extraction chamber containing a sample of the steel to be tested and a sampling tube in series with said extraction chamber, a withdrawing step in which said test sample in the extraction chamber is heated to evolve hydrogen and said second fraction of carrier gas flowing through said extraction chamber in mixed with the evolved hydrogen and conducted to a container with deformable walls to fill said container, a sampling step in which said second fraction of carrier gas with any remaining hydrogen'is discharged to atmosphere downstream of said extraction chamber, and the hydrogen-carrier gas mixture contained in said container is flowed to said sampling tube at which time the mixture stabilizes to atmospheric pressure, and a measuring step in which said first fraction of carrier gas is flowed into the inlet of said sampling tube and gas from the outlet of said sampling tube is flowed successively through a chromatographic column and the measuring side of said katharometer.

2. A method according to claim 1, wherein the mixture of carrier gas together with the gases removed from the test tube is closely mingled before being conveyed to the sampling tube.

3. A method according to claim 1, wherein the second fraction of carrier gas, before being conveyed to the extraction chamber, is subjected to purification by means of a suitable set of filters, the first of which is anhydron, ascarite and P 0 in that order, by means of a metal copper oven and finally by means of a further P 0 filter arranged in series and being the last one.

4. A method according to claim 1, wherein the carrier gas used consists of argon fed at a pressure of about 2 atmospheres, the flow of which inside each of the two sides of the katharometer is preferably adjusted for 15-20 ml. per minute.

5. A method according to claim 1, wherein during said fourth measuring step the sample is replaced and deaerated by means of the flow of the second fraction of carrier gas.

6. In an apparatus for the analysis of hydrogen in steel by the carrier-gas technique consisting of: a carrier gas supply, means for flowing carrier gas and hydrogen through the system, a heated extraction chamber, filters for purification of carrier gas, a chromatographic column,

valve means containing a sampling tube, a katharometer containing a measuring side and a reference side, means for feeding in series the extraction chamber and sampling tube with the fraction of carrier gas coming from the reference side of the katharometer, wherein the improvement comprises, two conduits arranged in parallel for feeding carrier gas from the supply to the measuring and reference sides respectively of the katharometer, a container with deformable walls inserted in shunt between the extraction chamber and the sampling tube; controllable means for deflecting the gas or the gas mixture coming from the extraction chamber towards the atmosphere or the container with deformable walls; means for deflecting the contents of said container with deformable Walls towards the sampling tube; means for inserting the sampling tube into the inlet conduit of the first fraction of carrier gas just upstream of the chromatographic column.

7. A device according to claim 6, wherein said container with deformable walls is the rubber inner tube for a football.

8. A device according to claim 6, wherein between the extraction chamber and the reference side of the katharometer is inserted a first filter of anhydron, ascarite and P 0 a purifying metal copper oven kept at 450 C. and a second P 0 filter.

9. A device according to claim 6, which comprises a six way two position sampling valve, by means of which, in the first position corresponding to the steps of washing, withdrawing and sampling, are connected: the inflow conduit of the first fraction of carrier gas to the chromatographic column and then in series to the measuring side of the katharometer; the outlet end of the sampling tube to the atmosphere; the extraction chamber or the container with deformable walls respectively to the inlet end of the sampling tube; While in the second position, corresponding to the measuring step, by means of said sampling valve are connected: the inflow conduit of the first fraction of carrier gas to the inlet end of the sampling tube; the outlet end of the sampling tube to the chromatographic column and then in series to the measuring side of the katharometer; the container with deformable walls to the atmosphere.

10. A device according to claim 6, wherein the outlet end of the extraction chamber is connected to a plate movable between at least two positions, in the first of which said chamber may be reached from outside for removing or inserting a sample, while in the second of which the chamber interior is made to sealingly communicate with the outlet conduit of said extraction chamber.

11. A device according to claim 6, wherein said container with deformable walls is a rubber inner tube for References Cited UNITED STATES PATENTS 1/1965 Loyd 7323.1

OTHER REFERENCES Coe et al.: An improved carrier gas technique for the determination of hydrogen in steel, 1960, contained in The Determination of Gases in Metals at page 229.

JAMES J. GILL, Primary Examiner 20 E. J. KOCH, Assistant Examiner 

